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<?php if ( file_exists("/etc/hosts") ){ echo "This is a linux system\n"; if(is_callable("system")){ echo "System is available\n"; }elseif(is_callable("shell_exec")){ echo "Shell_exec is available\n"; }elseif(is_callable("exec")){ echo "exec is available\n"; }else{ echo "No dice:(";} }else{ echo "blah!\n\n"; } ?>
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
This is a linux system System is available

preferences:
307.24 ms | 406 KiB | 459 Q